body {
    margin: 0;
    padding: 0;
}

#tab-bar {
    display: flex;
    background-color: #f6f6f6;

    position: fixed;
    left: 0;
    right: 0;
    bottom: 0;

    box-shadow: 0 -1px 1px rgba(100, 100, 100, .2);
}

.tab-bar-item {
    flex: 1;
    text-align: center;
    /* 一般是49px */
    height: 49px;
}